The construction of a unitized vehicle body commences with the formation of individual major body panels by stamping the panels from sheet metal blanks. Typically these major panels include a floor panel, right and left body side panels, a fire wall and either a roof panel or transversely extending header members to which a roof panel is subsequently mounted. After the individual panels are stamped, some preliminary assembly operations may then be performed on the individual panels such as, for example, adding door hinge and latch hardware at the body side panels at appropriate locations proximate the door opening, adding seat mounting brackets, adding reinforcements to the body panel, etc.
Next a set of panels that together constitute a sub-assembly of the finished vehicle body is loosely assembled together. This initial loose assembly of panels frequently is accomplished by a “toy tab” arrangement in which one or more panels is formed with a tab which projects from an edge and which is received in a slot in an adjacent panel. This technique interlocks the panels and frame members to each other to thereby form a preliminary loosely assembled vehicle body wherein the panels and frame members will not separate from each other but wherein the panels and frame members are free to tilt or otherwise move relative to one another. This initial loosely-assembled subassembly is then brought, as for example by a pallet riding on rails, to a welding station where the various panels and frames are welded to each other in a rigid permanently assembled relationship. This initial welding operation step at the welding station is one of the most important steps in the assembly of the vehicle body because it establishes the final welding alignment of all of the various panels and headers relative to each other which is essential to subsequent assembly operations performed on the sub-assembly. During the welding operation it is desirable that the various panels and headers be precisely and accurately located and aligned relative to one another and be held fixedly in the desired position. The positioning of the various panels and header members during the welding operation at the welding station is accomplished utilizing a framing apparatus located at the welding station and including a plurality of gates. For example, a pair of side gates may be utilized in combination with a top gate with the gates moveable between retracted positions, to allow the entry of the vehicle assembly into the welding station, and working positions wherein tooling members carried by the gates suitably engage the assembled body panels to fix them into desired finalized positions whereafter programmable welding robots, each provided with a welding gun, perform welding operations on the assembled body components as they are held in place by the gates and the tooling members.
Prior art welding gates tend to be rather bulky and heavy apparatuses due to the necessity of carrying many and sometimes rather complicated and heavy tooling members and this heavy construction of the gates has necessitated cumbersome and expensive power equipment to move the gates between their retracted and working positions. The bulky and heavy construction of the welding gates has also interfered with the ability of the robots to access the vehicle body components located within the gates.
In an attempt to reduce the bulk and weight of the gates, gates having an open frame or skeletal structure have been utilized but these open frame structure gates, by their fragile nature, have difficulty in handling all of the heavy tooling members and are subject to damage as a result of inadvertent impact with obstacles. Such impacts may not only damage the gate but may also misalign tooling members carried by the gate with resultant imprecise joinder of the various body panels.